The second period of the program, 1. continues investigations of the contractile mechanism common to cardiac and other muscles, 2. focuses on some mechanisms--light chain phophorylation and role of creatine kinase--seemingly specific to heart, and 3. exploits a new liposome technique (developed in the first period) for muscle physiology. Experiments in 1. examine by various fluorescence correlation and relaxation techniques whether myosin cross-bridges cycle, and also some of the myosin and actin processes that cause the cycling.